Congenital deficiency of sucrase-isomaltase is a disorder that affects the ability of a person to digest certain disaccharides, particularly saccharose, maltose and other disaccharides composed of these molecules. Disaccharides are broken down into simple sugars during digestion. Sucrose is decomposed into glucose and fructose. Meanwhile, maltose is broken down into two glucose molecules.

Usually in affected individuals, the alteration occurs when the individual begins to consume fruits, juices and cereals. After ingestion of sucrose or maltose, affected individuals manifest abdominal pain, bloating, diarrhea and excess gas. These digestive problems can lead to growth retardation and malnutrition. Most affected children are able to tolerate sucrose and maltose as they get older.

Congenital deficiency of sucrase-isomaltase is due to mutations in the SI gene, located on the long arm of chromosome 3 (3q25.2-q26.2). This gene encodes the enzyme sucrase-isomaltase. This enzyme is found in the intestine and is responsible for cleavage of sucrose and maltose disaccharides to their corresponding components to be absorbed in the small intestine. The sucrase-isomaltase enzyme is found on the surface of intestinal epithelial cells. These cells have microvilli that absorb nutrients from food as they pass through the intestine. The role of sucrase-isomaltase is decomposed sucrose and maltose into simple sugars that can be absorbed by the microvilli of intestinal epithelial cells.

They have identified at least 10 mutations in the SI gene in individuals with congenital deficiency of sucrase isomaltase. These mutations alter the folding and processing of the enzyme sucrase-isomaltase, transport within the intestinal epithelial cells, their orientation on the cell surface, or operation. An alteration in any of these cellular processes resulting in a sucrase-isomaltase enzyme can not properly decompose sucrose, maltose and other compounds made from these sugar molecules. The inability to digest these sugars causes intestinal discomfort that manifests itself in people with congenital sucrase-isomaltase.

This disease is inherited in an autosomal recessive pattern, that is, both copies of the gene in every cell must have mutations for alteration is expressed. The parents of an individual with an autosomal recessive disease have a copy of the mutated gene, but usually show no signs and symptoms of the disease.

Tests in IVAMI: in IVAMI perform detection of mutations associated with congenital sucrase-isomaltase by complete PCR amplification of the exons of the SI gene, and subsequent sequencing.

Samples recommended:EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).